ABSTRACT

Context Blood pressure (BP) measurement in clinicians' offices with a mercury
sphygmomanometer has numerous drawbacks. In contrast, the use of home BP measurement
improves measurement precision and reproducibility. However, data about its
prognostic value are lacking.

Objective To assess the prognostic value of home vs office BP measurement by general
practitioners in a European population of elderly patients being treated for
hypertension.

Design, Setting, and Participants Office and home BP and cardiac risk factors were measured at baseline
in a cohort of 4939 treated hypertensive patients (mean age, 70 [SD, 6.5]
years; 48.9% men) who were recruited and followed up by their usual general
practitioners without specific recommendations about their management. The
cohort was then followed up for a mean of 3.2 (SD, 0.5) years. The thresholds
defining uncontrolled hypertension were at least 140/90 mm Hg for office BP
and 135/85 mm Hg for home BP.

Main Outcome Measures The primary end point was cardiovascular mortality. Secondary end points
were total mortality and the combination of cardiovascular mortality, nonfatal
myocardial infarction, nonfatal stroke, transient ischemic attack, hospitalization
for angina or heart failure, percutaneous transluminal coronary angioplasty,
or coronary artery bypass graft surgery.

Results At the end of follow-up, clinical status was known for 99.9% of patients.
At least 1 cardiovascular event had occurred in 324 (incidence, 22.2/1000
patient-years). For BP self-measurement at home, each 10-mm Hg increase in
systolic BP increased the risk of a cardiovascular event by 17.2% (95% confidence
interval [CI], 11.0%-23.8%) and each 5-mm Hg increase in diastolic BP increased
that risk by 11.7% (95% CI, 5.7%-18.1%). Conversely, for the same increase
in BP observed using office measurement, there was no significant increase
in the risk of a cardiovascular event. In a multivariable model with patients
having controlled hypertension (normal home and office BP) as the referent,
the hazard ratio of cardiovascular events was 1.96 (95% CI, 1.27-3.02) in
patients with uncontrolled hypertension (high BP with both measurement methods),
2.06 (95% CI, 1.22-3.47) in patients with normal office BP and elevated home
BP, and 1.18 (95% CI, 0.67-2.10) in patients with elevated office BP and normal
home BP.

Conclusions Our findings suggest that home BP measurement has a better prognostic
accuracy than office BP measurement. Blood pressure should systematically
be measured at home in patients receiving treatment for hypertension.

Figures in this Article

The reference method for blood pressure (BP) measurement during clinical
consultations is the auscultatory method with a mercury sphygmomanometer.
This method has been used to demonstrate the relationship between BP and cardiovascular
risk. A meta-analysis of individual data from almost 1 million adults participating
in 61 prospective studies precisely established the prognostic value of this
method of measurement: for each increase of 10 mm Hg in systolic BP (SBP)
or 5 mm Hg in diastolic BP (DBP), the average risk of cerebrovascular mortality
increases by 40% and the risk of mortality from ischemic heart disease by
30%.1 The mercury sphygmomanometer, used during
clinical consultations, is also the tool that has demonstrated the benefit
of antihypertensive treatment. In the first meta-analysis of randomized controlled
trials using the sphygmomanometer, a decrease in DBP of 5 mm Hg to 6 mm Hg
was associated with a 42% reduction in the risk of stroke syndrome and a 14%
reduction in the risk of coronary events.2

There are, however, numerous criticisms of clinical BP measurement.
Major interobserver and intraobserver variability exists, related to the difficulty
of standardizing the measurement conditions and the insufficiency of the number
of measurements. There is considerable variability among individual examiners;
subjectivity can be related to hearing, sight, a preference for rounding digits
during measurement, etc.3 It fails to recognize
"white-coat hypertension," also known as "office hypertension."4 Finally,
the mercury sphygmomanometer should probably be abandoned for ecological reasons
(ie, the toxicity of mercury). Replacement of office BP measurement with physician-independent
methods (ambulatory BP monitoring and home BP self-measurement) is advocated
by many guidelines.

Perloff et al5 and Verdecchia et al6 demonstrated the better prognostic value of ambulatory
BP monitoring than office measurement in a general untreated population, and
Clement et al7 did so in patients being treated
for hypertension. Home BP has a high degree of measurement quality and is
cheaper and better accepted by patients than ambulatory BP monitoring.8 To date, there has been only 1 prognostic study of
cardiovascular morbidity and mortality suggesting that this method is superior
to office BP measurement. This study involved a normotensive Asian population
living in a rural area and used a self-measurement protocol different from
that in usual practice.9 We therefore instituted
a cohort study to evaluate the prognostic value of home BP measurement and
that of office BP measurement by general practitioners in a European population
of patients being treated for hypertension.

METHODS

Study Design

The SHEAF (Self-Measurement of Blood Pressure at Home in the Elderly:
Assessment and Follow-up) study was a 3-year prospective cohort study designed
to assess in general practice whether the prognostic value of home BP is greater
than that of office BP. The study comprised 2 successive phases. The first
phase consisted of a period of evaluation with 2 separate visits at an interval
of 2 weeks. Office and home BP and heart rate (the mean of heart rate values
measured at home) were recorded, as well as presence of antihypertensive treatment
and demographic and medical history characteristics; ie, sex, age, obesity
(body mass index ≥30), smoking status (current, former, or never), presence
of diabetes mellitus, presence of treated hypercholesterolemia (fibrates or
statins), history of cardiovascular events, and creatinine clearance (using
the formula of Cockroft and Gault10). The second
phase was a 3-year follow-up of patients. This was an observational study,
and, therefore, there was no specific recommendation with regard to management
of hypertension, including frequency of visits, type of drug treatment or
BP goal, and no data were recorded concerning BP level or antihypertensive
drug use during the follow-up.

The practitioners were instructed to carefully report and document all
outcome events that occurred during the follow-up and were asked each year
about the morbidity and mortality status of the patients. In case of no response,
practitioners and then patients were telephoned by a study physician. If no
contact could be established, a query was sent to the city hall (registry
of births and deaths) of the town in which the patient was born to determine
deaths. Study end points were identified by an end-point committee.

Approval, Support, and Conduct of the Study

The protocol was approved by the French National Data Protection Committee
(Commission Nationale Informatique et Liberté) and conducted in accordance
with the Declaration of Helsinki. All participants were informed about the
study and gave oral consent.

Setting and Patient Recruitment

Patients of both sexes were recruited by general practitioners and were
included in the study if they fulfilled the following criteria: age at least
60 years; primary permanent hypertension defined by the receipt of antihypertensive
treatment or, in the absence of treatment, by office BP values greater than
140/90 mm Hg measured at 2 separate times during the year preceding inclusion;
arm size allowing the use of a standard cuff; ability to perform an appropriate
number of BP measurements at home with the study device; and absence of any
threatening disease or recent acute cardiovascular event (eg, myocardial infarction,
stroke). We did not ask general practitioners to record information about
patients who fulfilled criteria inclusion but were not included in the study.

End Points

The primary end point was cardiovascular mortality. Secondary end points
were total mortality and the combination of cardiovascular mortality, nonfatal
myocardial infarction, nonfatal stroke, transient ischemic attack, hospitalization
for angina or heart failure, percutaneous transluminal coronary angioplasty,
and coronary artery bypass graft surgery.

The end-point committee, comprising a cardiologist, an internist, and
a neurologist, identified all major end points by reviewing the patient discharge
summaries and source documents. Complementary documentation was requested
if necessary by this committee. The committee was blinded with respect to
all BP data. Cardiovascular events were validated according to the principles
used in randomized trials. The following definitions were used:

Stroke was defined as a neurologic deficit with
symptoms continuing for more than 24 hours or leading to death with no apparent
cause other than vascular. Transient ischemic attack was defined as a neurologic
deficit lasting less than 24 hours.

Acute myocardial infarction was defined by the
presence of 2 or more of the following: typical chest pain, electrocardiographic
changes, and increased cardiac enzyme concentrations. The definition of myocardial
infarction did not include silent myocardial infarction.

Sudden death was defined as any death of unknown
cause occurring immediately or within 24 hours after onset of acute symptoms
or any unwitnessed death for which no likely cause could be established on
the basis of medical history.

Angina pectoris was diagnosed if there was hospitalization
and chest pain and documented electrocardiographic signs of coronary ischemia
or if there was a need for coronary revascularization in the absence of acute
myocardial infarction.

An event was considered validated when all 3 members
of the end-point committee agreed on the diagnosis.

BP Measurements

Office BP Measurement. During the first phase,
triplicate BP measurements were taken at both visits by the physicians, using
a mercury sphygmomanometer with the patient in the sitting position after
a 5-minute rest, without specific training. No recommendation about time of
measurement was made to the physicians. Systolic BP was measured at phase
1 of Korotkoff sounds and diastolic BP at phase 5 of Korotkoff sounds. The
mean of the 6 readings was taken as the office baseline BP for each patient.

Home BP Measurement. Home BP measurement was
performed during the initial phase of the study. Home BP measurements were
planned over a 4-day period chosen at the patient's convenience. Every day,
a series of 3 consecutive measurements was requested in the morning (8 AM) and repeated in the evening (8 PM). Measurements
were performed in the sitting position after a 5-minute rest. The Omron-705
CP device (Omron Corp, Tokyo, Japan), which is a printer-equipped, semiautomatic,
digitized device based on the oscillometric method, was used by all participants.
This device had been previously validated against a mercury sphygmomanometer
according to the revised protocol of the British Hypertension Society.11 Because it has been shown that the degree of reliability
of hypertensive patients' reporting of self-measured BP values is both variable
and unpredictable,12 each patient was asked
to write their measurement results in a booklet designed for the study and
to keep all printouts and staple them in the booklet.

Home BP Data Management

For each patient, aberrant values were deleted according to the following
predefined rules: DBP less than 40 mm Hg or more than 150 mm Hg; SBP less
than 60 mm Hg or more than 250 mm Hg; and pulse pressure less than 10 mm Hg.
Measurements performed outside of the predefined morning and evening time
frames (4-12 AM range or 4-12 PM range) were
also discarded.

Patients were included in the study only if they had at least 15 valid
measurements, with at least 6 measurements in the morning and 6 measurements
in the evening. For each included patient, the mean of all the available home
measurements was taken as the home BP value and used for comparison with office
measurements.13

Data and Statistical Analyses

Sample Size and Patient Recruitment. The calculation
of the sample size of the cohort was based on an assumed cardiovascular death
rate of 0.5% to 1.0% per year in elderly patients with hypertension in France,
giving an estimated total 3-year number of 15 to 30 deaths per 1000 included
patients. On the basis of a ratio of 1 nonfatal event to 1 death, we anticipated
30 to 60 events per 1000 included patients. According to Peduzzi et al,14 the accuracy and precision of the coefficients estimated
by the proportional hazards method are low when the number of events per variable
is less than 10. Since we anticipated a model comprising 10 to 15 variables,
at least 150 events should be observed. We therefore decided to include 5000
patients to observe a total 3-year number of 150 to 300 events.

From February 1998 to March 1999, 1429 general practitioners recruited
5649 patients. Among these patients, 186 were excluded for age younger than
60 years and 252 for nonvalid home BP measurements. Thus, 5211 patients (2565
men and 2646 women) with a mean age of 70 years (SD, 7 years) and valid home
BP measurements were included. A total of 4939 (95%) were being treated with
at least 1 antihypertensive drug. Characteristics of treated and untreated
patients were comparable.13 For homogeneity
purposes, further analyses were performed only in the 4939 treated patients
(Figure 1).

Figure. Flow of Study Participants

BP Thresholds. We formed subgroups of patients
with hypertension according to the following rules: For the office BP measurement,
the internationally accepted limit of 140/90 mm Hg was adopted4 and
for the home BP measurement, the internationally accepted limit of 135/85
mm Hg was adopted.15 Patients were classified
into 4 subgroups: those with "controlled" hypertension (ie, BP below the limit
for each of the methods); those with "uncontrolled" hypertension (ie, BP greater
than or equal to the limit for each of the methods); those with BP below the
limit of normality of the home BP measurement and greater than or equal to
the limit of normality of the office BP measurement; and those with BP below
the limit of normality of the office BP measurement and greater than or equal
to the limit of normality of the home BP measurement.

Prognostic Value of Home BP. The prognostic
value of home BP was analyzed at the time of the first composite end point
occurring during follow-up. Hazard ratios (HRs) with 95% confidence intervals
(CIs) were estimated using the Cox proportional hazards model after adjustment
for sex, age, heart rate (mean of values measured during the series of home
BP measurements), smoking status (current vs former or never), history of
cardiovascular events, presence of diabetes mellitus, presence of obesity,
and presence of treatment of hypercholesterolemia. Separate models were used
for office and home BP and for SBP and DBP, after verification of the hypothesis
of the proportional risk. For the analysis of the prognoses of the 4 subgroups
individualized according to BP thresholds, the HRs were calculated in a multivariable
(Cox) model with the group of patients with controlled hypertension as the
referent.

Quantitative data are summarized as mean (SD) and qualitative data as
percentages. Unpaired t tests were used for normally
distributed data and comparisons of 2 groups, and analysis of variance for
comparisons of more than 2 groups. The χ2 test was used for
categorical data.

The analyses were performed using SAS software, version 8.2 (SAS Institute
Inc, Cary, NC). For all analyses, P<.05 was considered
statistically significant.

RESULTS

General characteristics of the 4939 patients treated for hypertension
are shown in Table 1. Inclusion
was limited to those with valid measurements to avoid bias due to a variable
number of measurements that could influence precision of home BP estimates.
As required in the protocol, the mean of 6 measurements defined office BP,
and the mean number of measurements used to define home BP was 27 (SD, 5).
At baseline, only 13.9% appeared to have their hypertension controlled by
both measurement methods, 13.3% had elevated BP in the office but not at home,
9.4% had elevated BP at home but not in the office, and 63.4% had uncontrolled
hypertension by both measurement methods.

The follow-up of the study ended in early 2002. The vital status was
known for 4932 patients (99.9%) at the end of a mean follow-up of 3.2 (SD,
0.5) years (93.1% had a follow-up >2.5 years). In terms of cardiovascular
morbidity and mortality, the status was known for 4928 patients (99.78%) at
the end of a mean follow-up of 3.0 (SD, 0.6) years (88.8% had a follow-up
>2.5 years).

There were 205 deaths (incidence, 13.6/1000 patient-years), of which
85 were of cardiovascular origin (incidence, 5.6/1000 patient-years). The
causes of death and their respective frequencies are listed in Table 2.

In the cohort, 324 patients had at least 1 cardiovascular event, used
for the analysis of morbidity and mortality (incidence, 22.2/1000 patient-years).
The origins of the cardiovascular events and their respective frequencies
are listed in Table 3.

We also used a model with the same predictors but with increments of
5 mm Hg and 10 mm Hg (rather than 1 mm Hg) for DBP and SBP, respectively.
Using this model for home BP self-measurement, for each increase in SBP of
10 mm Hg, the risk of a cardiovascular event increased by 17.2% (95% CI, 11.0%-23.8%)
and for each increase in DBP of 5 mm Hg, the risk of a cardiovascular event
increased by 11.7% (95% CI, 5.7%-18.1%). Conversely, after adjustment for
the same predictors, for the same increases in BP observed using office measurement,
there was no significant increase in the risk of an event (5.8% increase;
95% CI, −0.8% to 12.5% and 1.4% increase; 95% CI, −4.8% to 7.9%,
respectively). Irrespective of the measurement method, BP was not significantly
related to either cardiovascular mortality or total mortality.

The incidence of cardiovascular events in patients with elevated BP
in the office but not at home was the same as that of patients considered
to have their hypertension controlled: 11.1 and 12.1 cases per 1000 patient-years,
respectively. Conversely, the incidence of cardiovascular events in patients
with elevated BP at home but not in the office was high and similar to that
of patients with uncontrolled hypertension (30.6 and 25.6 cases per 1000 patient-years,
respectively) (Table 6). In a
multivariable model using patients with controlled hypertension as the referent,
the HR of cardiovascular events was double for patients with uncontrolled
hypertension (HR, 1.96; 95% CI, 1.27-3.02) and for patients with elevated
BP at home but not in the office (HR, 2.06; 95% CI, 1.22-3.47), whereas the
HR of patients with elevated BP in the office but not at home did not differ
(HR, 1.18; 95% CI, 0.67-2.10).

COMMENT

In this cohort study conducted among patients aged 60 years or older
being treated for hypertension in general practitioners' offices, home BP
self-measurement defines the prognosis in terms of cardiovascular morbidity
and mortality better than office measurement. In this study, home BP self-measurement
identified a very specific subgroup of 9% of patients with poor control of
their hypertension at home that appeared controlled in the physician's office.
The initial profile (in terms of risk factors and previous cardiovascular
history) of patients with elevated BP at home but not in the office is similar
to that of patients considered to have uncontrolled hypertension by both measurement
methods.13 This study adds new information
that their cardiovascular prognoses are comparable. In the cross-sectional
part of this study, at the time of inclusion, the profile of the 13% of patients
with elevated BP in the office but not at home was similar to that of patients
considered to have controlled hypertension by both measurement methods.13 This study also shows that their cardiovascular prognoses
are comparable. Therefore, cross-sectional observation is confirmed by a prospective
cohort study.

One of the strengths of the study is that these results were obtained
in a large patient population by a prospective cohort study with exhaustive
collection of information on morbidity and mortality status. In addition,
all the events that occurred were validated in terms of precise criteria predefined
by an independent validation committee blinded to the results of the office
and home BP measurements. The general practitioner investigators were aware
of the results of the home BP measurement performed at baseline but were not
given any specific recommendations for management of hypertension, either
in terms of utilization of the results, of BP target ranges, or of therapeutic
procedures. It is therefore unlikely that, over a 3-year period, these results
might have influenced the behavior of the general practitioners, but we cannot
confirm this in the absence of collection of data relating to the changes
in antihypertensive treatment during follow-up. The same limitation is present
in the study by Clement et al,7 who demonstrated
that ambulatory BP monitoring had a better prognostic value than office measurement
in patients treated for hypertension.

It is unlikely that a systematic relationship between timing of antihypertensive
drug ingestion and that of BP measurement could explain the better values
of home over office BP measurement, although we did not record data on these
2 parameters. Thus, home BP measurement is the mean of BP trough (morning)
and peak (evening) values. Since office BP measurement was performed during
the usual working hours of general practitioners, it is likely that every
possible timing of measurement is represented in our large sample.

A large enough number of morbidity and mortality events enable the prognostic
superiority of standardized home BP measurement to be demonstrated. Superiority
is related to the reduced intrapatient variability compared with the office
BP measurement,16- 18 itself
due to the increased number of measurements; 27 measurements defined home
BP while only 6 measurements defined office BP. This result is also due in
part to poor performance of office BP measurement; for example, a marked preference
to round measurement digits.3 The lack of prognostic
value of home BP measurement for cardiovascular mortality and total mortality
is probably related to the lower incidence of cardiovascular mortality in
this population of patients treated for hypertension, as expected, and/or
to a shorter follow-up than that of many epidemiological studies. The lack
of relationship between BP levels measured by the physician and the incidence
of cardiovascular morbidity and mortality contrasts with the data from the
largest meta-analysis, which includes 958 074 individuals with a larger
range of BP and followed up for a longer time, giving it substantial statistical
power.1

The Japanese study by Ohkubo et al9 is
the only other prospective study of home BP self-measurement. This study followed
up 1789 patients for 6.6 years. As with the SHEAF study, the authors found
no association between BP level measured in the physician's office and incidence
of cardiovascular mortality. They demonstrated a relationship between the
SBP level measured at home and incidence of total mortality on one hand (HR,
1.01; 95% CI, 1.00-1.03) and cardiovascular mortality on the other hand (HR,
1.02; 95% CI, 1.00-1.04). For each increase in SBP of 10 mm Hg, an increase
of 23% was noted in the risk of cardiovascular mortality. Conversely, there
was no relationship between DBP and global or cardiovascular mortality.

The SHEAF study confirms in patients treated for hypertension the prevalence
and favorable prognosis of the "white coat effect" (elevated BP in the office
but not at home) that has already been indicated by studies conducted initially
with ambulatory BP measurement in untreated patients.6,19,20 The
new element relates to masked hypertension (elevated BP at home but not in
the office), a term proposed by Pickering et al21 in
preference to the term of "reverse white-coat hypertension" or "isolated home
hypertension." The reproducibility of this classification has not been evaluated
and the mechanisms of this phenomenon are not known.21,22 According
to the available studies using either ambulatory measurement23- 25 or
home self-measurement and ambulatory measurement,26 and
including either patients with hypertension or a general population, this
phenomenon is observed in 7% to 45% of the participants studied. Pickering
et al suggest that this frequency decreases with age,21 which
corroborates the fairly low frequency observed in our 70-year-old population.
Pickering et al noted, like us, that patients with masked hypertension are
more often women and have a high frequency of conventional cardiovascular
risk factors (eg, age, obesity, hypercholesterolemia, hyperglycemia).23 In particular, these patients have a greater frequency
of damage to target organs (left ventricular mass index and presence of carotid
plaques).23 In a recent analysis of the data
from the PAMELA study, from which individuals being treated for hypertension
were excluded, 67% were normotensive, 12% were hypertensive, 12% had white-coat
hypertension, and 9% had masked hypertension. Here again, the left ventricular
mass index was higher in those with masked hypertension and hypertension than
in normotensive individuals.23 These data concerning
surrogate end points suggested an adverse effect of masked hypertension.21,22 A recent prospective study of 578
untreated elderly men confirms the adverse effect of masked hypertension determined
by ambulatory BP monitoring. In a multivariable analysis that took into account
serum cholesterol levels, smoking, and diabetes, both isolated ambulatory
hypertension (HR, 2.77; 95% CI, 1.15-6.68) and sustained hypertension (HR,
2.94; 95% CI, 1.49-5.82) were independent predictors of cardiovascular morbidity.27 These results are in keeping with those of the SHEAF
study, which demonstrates the severity of elevated BP at home but not in the
office in treated patients.

In conclusion, home BP self-measurement has a better prognostic value
than office BP measurement. In this elderly population, office BP measurement
failed to identify 13% of patients with elevated BP in the office but not
at home with a good prognosis and 9% of those with elevated BP at home but
not in the office with a poor prognosis. The frequency of this double error,
which is both diagnostic (with respect to the control of hypertension) and
prognostic (with respect to the incidence of cardiovascular events), suggests
that the monitoring of patients being treated for hypertension must include
home BP self-measurement, which is the method preferred by patients,8 with an excellent feasibility.28 It
remains to be shown that the adaptation of treatment to the results of home
BP self-measurement allows better cardiovascular prevention than adaptation
of treatment to results of measurements in the physician's office. Treatment
and follow-up of patients with elevated BP at home but not in the office need
to be studied.

Ohkubo T, Imai Y, Tsuji I.
et al. Home blood pressure measurement has a stronger predictive power for
mortality than does screening blood pressure measurement: a population based
observation in Ohasama, Japan. J Hypertens.1998;16:971-975.PubMed

Ohkubo T, Imai Y, Tsuji I.
et al. Home blood pressure measurement has a stronger predictive power for
mortality than does screening blood pressure measurement: a population based
observation in Ohasama, Japan. J Hypertens.1998;16:971-975.PubMed

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